It has been repeatedly demonstrated by correlating scalp-recorded EEG with intracranial neuronal discharges in the monkey and the cat, that the polarity of ERPs, are related to either excitation or inhibition of cells. Comparison of evoked potentials and neuronal spiking activity reveals that neuronal discharges/firing in thalamocortical cells seem to result in negative ERP components, while cellular inhibition underlies positive potentials. Thus EPSPs/depolarisations appear responsible for negative ERP deflections, while IPSPs/hyperpolarisations are the cause of scalp-recorded positivities. Specifically, the scalp recorded negative shifts seem to be due to the depolarisation of pyramidal cell dendrites, which results in an extracellular surface current sink, with the opposite situation the case for scalp recorded positives. The relationship between neuronal activity and scalp-recorded potentials is shown in Figures 2.5 and 2.6 above, from Coenen (1995). Although this polarity reversal between intracranial and scalp recorded activity is true in most cases, the opposite relationship, where scalp positives are due to neuronal excitation and negatives to inhibition, has also been found on occasion.

It has been repeatedly demonstrated by correlating scalp recorded EEG with intracranial neuronal discharges in the monkey and the cat that the polarity of ERPs are related to either excitation or inhibition of cells. Comparison of evoked potentials and neuronal spiking activity reveals that neuronal discharges/firing in thalamocortical cells seem to result in negative ERP components, while cellular inhibition underlies positive potentials. Thus EPSPs/depolarisations appear responsible for negative ERP deflections, while IPSPs/hyperpolarisations are the cause of scalp-recorded positivities. Specifically, the scalp recorded negative shifts seem to be due to the depolarisation of pyramidal cell dendrites, which results in an extracellular surface current sink, with the opposite situation the case for scalp recorded positives. The relationship between neuronal activity and scalp-recorded potentials is shown in Figures 3 and 4, from Coenen (1995). Although this polarity reversal between intracranial and scalp recorded activity is true in most cases, the opposite relationship, where scalp positives are due to neuronal excitation and negatives to inhibition, has also been found on occasion.